1. Field of the Invention
The present invention relates generally to the field of optical communications, and more particularly to an optical wavelength multiplexer, demultiplexer, or transceiver.
2. Technical Background
In a wavelength division multiplexed optical system, independent optical signals from several sources, each having a different central wavelength, are combined and introduced into a single optical fiber. In this fashion, the data transmission capacity of the optical fiber is increased by a factor equal to the number of multiplexed signals. The multiplexed signals may be separated into the independent wavelength signals by a device known as a demultiplexer. Demultiplexers generally use wavelength-selective optical elements such as diffraction gratings or interference filters to separate a demultiplexed optical signal into its component wavelengths.
For use in local area network and fiber to the home applications, small, inexpensive multiplexing and demultiplexing components are required. To provide devices with reduced cost and a high level of integration and miniaturization, molded plastic bodies having integral mirrors and lenses may be combined with interference filters. One such device is described in U.S. Pat. No. 6,198,864, granted to Lemoff et al. This device includes a molded optical body having a relay arrangement of reflective focusing lenses, and a plurality of wavelength-specific filters connected to an output of the body. A multiplexed optical signal is introduced into the molded optical body, propagates in a zig-zag fashion between the reflective focusing lenses and the filters, with one wavelength being transmitted through each filter to a detector. This device relies on reflections to guide the optical signals between interference filters. With each reflection, however, the optical signal can suffer beam distortion and misalignment as well as absorption and scattering loss, leading to decreased performance of the device. Also, as this device is about 7 mm in length, optical signals must traverse at least that distance in the molded optical body, leading to non-negligible absorption losses in the molded material.
Another device is described in U.S. Pat. No. 6,201,908, to Grann. This device has a molded optical body including a collimating lens for an input fiber, and an optical block with a flat, reflective upper surface, and a flat lower surface having a plurality of interference filters carried thereon. In this device, a multiplexed optical signal is collimated by the collimating lens, and is introduced into the optical block, where it propagates in a zig-zag fashion between the reflective upper surface and the filters, with one wavelength being transmitted through each filter into the molded optical body, where it passes through a molded focusing lens into a detector. This device also relies on multiple reflections to guide the optical signals to the interference filters, incurring loss at every reflection.
U.S. Pat. No. 6,219,470, granted to Tu, describes a multiplexing transmitter and receiver utilizing a micromachined silicon substrate as the mounting platform for discrete optical components and optoelectronic devices. This device requires photolithographic processing, as well as the fabrication and alignment of collimating lenses. In this device, there are several air/dielectric boundaries in the optical path, causing significant loss due to reflection.
Notwithstanding the current availability of transceiver components, there remains a need for low-cost integrated transceiver components for local area network and fiber to the home applications. The devices must be inexpensive to fabricate and assemble, must be highly stable to temperature fluctuations, and must be adaptable to a wide range of transmitted and received wavelengths.
One aspect of the present invention is an optical device for use with at least one optical signal, each optical signal having a wavelength within a unique wavelength band. The optical device includes at least three transceiver elements, each transceiver element being operatively coupled to a lensing element, and each transceiver element emitting at least one of the optical signals, receiving at least one of the optical signals, or both. The optical device further includes a filter subassembly having at least one prism, each prism having at least one substantially flat face, and at least one interference filter, each interference filter being deposited on one of the substantially flat faces of one of the prisms, each interference filter being selective between two of the unique wavelength bands of the optical signal. The optical device further includes a transparent mounting structure having at least one transceiver element alignment feature, each transceiver element being held in one of the transceiver element alignment features, and a filter subassembly alignment feature, the filter subassembly being held in the filter subassembly alignment feature. Each optical signal is coupled from one of the transceiver optical elements to another of the transceiver optical elements by at least one of the interference filters.
Another aspect of the present invention is an optical device for use with a plurality of optical signals, each optical signal having a wavelength within a unique wavelength band. The optical device includes at least three transceiver elements, each transceiver element being operatively coupled to a lensing element, and each transceiver element emitting at least one of the optical signals, receiving at least one of the optical signals, or both. The optical device further includes at least one prism, each prism having at least one substantially flat face. The optical device further includes at least one interference filter, each interference filter being deposited on one of the substantially flat faces of one of the prisms, each interference filter being selective between two of the unique wavelength bands of the optical signal. The optical device further includes a transparent mounting structure having at least one transceiver element alignment feature, each transceiver element being held in one of the transceiver element alignment features, and at least one prism alignment feature, each prism being held in one of the prism alignment features. Each optical signal is coupled from one of the transceiver elements to another of the transceiver elements by at least one of the interference filters.
The devices of the present invention have many advantages over the prior art. The devices can operate as multiplexers, demultiplexers or transceivers. Reflections between interference filters are minimized, reducing losses due to reflection in the device. The path length of the optical signal in the mounting structure is minimized, reducing crosstalk and losses due to absorption losses in the mounting structure. Minimization of path length may also reduce scattering losses due to haze in the material of the mounting structure. The devices can be designed to have good performance over a wide range of temperatures. The devices of the present invention may be upgraded for different wavelengths or data rates without tool redesign. Further, the devices of the present invention can be fabricated and assembled using low-cost techniques, making them attractive for applications such as local area networks and fiber to the home.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description of recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.